Selective affinity material, preparation thereof by molecular imprinting, and use of the same

ABSTRACT

A selective adsorption material made by the process comprising: a) non-cavalently or reversibly-covalently binding a print molecule to at least two styrene, acrylate or silica monomers, each of which monomers brinds to said print molecule by means of a different functional group; b) immobilizing said bound monomers by being polymerized to each other in the presence of an effective amount of cross-linker; and c) removing said print molecule from said polymer by extraction to leave a cavity in said polymer which is stereo-tailored to a biological molecule of interest; and wherein said print molecule is the biological molecule of interest.

FIELD OF THE INVENTION

The invention relates to a selective adsorption material, especially suitable for adsorption of biological macromolecules, a process for preparing this selective adsorption material, and the use thereof for purification and analysis, especially of biological macromolecules.

BACKGROUND OF THE INVENTION

It Is known to prepare homogeneous gels while using the so-called molecular imprinting technique by making imprints of dyes (R. Arshady, K. Mosbach; Makromol. Chemie, 182 (1981) 687) and amino acid derivatives (L. Andersson, B. Sellergren, K. Mosbach, Tetrahedron Lett. 25 (1984) 5211). Merely non-covalent bonding between a “print molecule” and monomers is used. After polymerisation of the monomers and removal of the print molecule, a selective polymer is obtained, based on binding groups correctly immobilised in space and present in cavities which have the shape of a mould of the print molecule. A summary of this technique is given by B. Ekberg, K. Mosbach, in Trends Biotechnol., 7 (1989) 92.

It is known to make imprints of carbohydrate derivatives substituted with covalently, but reversibly bonded vinylphenyl boric acid groups, so-called boronate esters, which after polymerisation have permitted hydrolysis and binding of a new print molecule (G. Wulff, ACS Symp. Series, 308 (1986) 186). Decisive of the selectivity of the thus prepared polymers are correctly positioned binding boronate groups and a well-shaped cavity. The drawback of this system is that a complicated chemical synthesis is necessary.

Prearranged boronate groups have also been used for Faking imprints of glycoprotein ((Transferrin, M. Glad, O. Norrlöw, B. Sellergren, N. Siegbahn, K. Mosbach, J. Chromatogr., 347 (1985) 11) and bis-nucleotides O. Norrlöw, M. O. Mánsson K. Mosbach. J. Chromatogr., 396 (1987) 374) on silica. In this context, use has been made of a mixture of non-covalently bonding organic silanes and boronate silane, which has been caused to interact with a print molecule before polymerisation on the surface. The effect of recognition seems mainly to depend on the fact that the boronate groups are correctly spaced from each other to be able to interact effectively with the print molecules. Transferrin has a total of four silica acid groups and bis-NAD has four riboses which form boronate esters.

It is also known to use, in affinity chromatography methods, adsorption material having specific ligands, but these are randomly localised on the sorbent and may therefore yield poor selectivity. Furthermore, there will be a large number of unused ligands, which is uneconomical from the industrial point of view.

Immobilised phenyl boric acid has been used to separate carbohydrate derivatives (H. L. Weith, J. L. Wiebers, P. T. Gilham, Biochemistry, 91 (1970) 4) and also to separate glycosylised hemoglobin and other glycoproteins (P. D. G. Dean, P. J. Brown, V. Bouriotis, U.S. Pat. No. 4,269,605 (1981).

For purification and analysis, especially of biological macromolecules, selectivity is most important. It is frequently necessary to distinguish a single component in a mixture of, maybe, several thousand components. The known adsorption materials are in most cases not sufficiently selective and cause non-specific binding, which may completely destroy the result of an analysis.

Modern biotechnical production and analysis as well as a large amount of medical diagnostics are based on selective binding. The methods known so far are also for these purposes not sufficiently selective and/or sufficiently simple to be economically useful on an industrial scale. Therefore there is a need of an adsorption material having very high selectivity and low non-specific binding, which may be prepared on a large scale and at low cost.

SUMMARY OF THE INVENTION

According to the invention, a selective adsorption material is provided, which is especially suitable for adsorption of biological macromolecules, and which is characterised In that it comprises immobilised ligands which have been localised to selectively adsorb a predetermined molecule by their first being bound to a print molecule which has then been removed after the immobilisation of the ligand.

The invention also comprises a process for preparing a selective adsorption material, especially suitable for adsorption of biological macromolecules, characterised in that a print molecule having at least two separate binding sites is bonded to the corresponding, at least two immobilisable ligands, that the ligands are immobilised, and that subsequently the print molecule is removed.

Finally the invention relates to the use of the selective adsorption material for purification or analysis, especially of biological macromolecules.

BRIEF DESCRIPTION OF THE DRAWINGS

The difference between a prior art adsorption material and the invention is schematically shown in the accompanying drawings in which:

FIG. 1 is a schematic sketch of a prior art sorbent with randomly positioned binding groups, e.g., boronate, immobilised, metal; and

FIG. 2 shows a sorbent according to the invention, with specifically localised, binding groups.

After prebinding to the print molecule and the subsequent immobilisation, the binding groups (ligands) will be bonded preferably to the surface of a matrix. The correct localisation of ligands on two dimensions results in increased selectivity by the print molecule having at least two separate binding sites. The corresponding, at least two immobilised ligands will thus be correctly spaced apart. This results in optimal binding of the target molecule in the subsequent adsorption.

As is evident from that stated above, the invention thus relates to a form of directed immobilisation of affinity ligands or other (chemical) ligands. This directed immobilisation is achieved by means of a prebinding method. The advantage as compared to randomly immobilised binding groups is that the print molecule is bonded more effectively and with greater selectivity. At the same time, all ligands may be utilised, thereby avoiding an excess thereof, which otherwise may easily result in non-specific bonding which in turn results in a lower yield.

Ligands which are useful for the invention should carry groups that can be bonded to a print molecule, and groups which can be used for immobilisation of the ligands. One type of suitable ligand is a monomer which can be immobilised by polymerisation. Examples of groups that can be bonded to a print molecule are given In Table 1.

TABLE 1 Group binding to print Binding group on print molecule on ligand/monomer molecule Imidazole-metal Histidine, tryptophane, thiol Iminodiacetic acid-metal ″ Carboxyl Amine Amine Carboxyl Carboxyl Carboxyl, amide (hydrogen bonding) Boronate Carbohydrate, diol Thiol Thiol Aldehyde Amine

Boronate, thiol and aldehyde are bonded covalently, whereas the other groups are bonded non-covalently to the print molecule.

Among groups that may be used for immobilisation, mention can be made of silanes which bind silanol and hydroxyl groups, and vinyl, acryl and methacryl which polymerise an a matrix.

Other ligands/monomers that may be used are:

-   Acryloyhistamine: H. Morawetz, W. R. Song, JACS, 88 (1966) 571. -   Boronate silane: M. Glad, O. Norrlöw, B. Sellergren, N. Siegbahn, K.     Mosbach, J. Chromatogr., 347 (1985) 11. -   IDA-silane: A. Figueroa, C. Corradini, B. Felbush, B. L. Karger, P.     Chromatogr., 371 (1986) 335.

Moreover, different types of ligands may be used simultaneously in one preparation. For example, use can be made of both boronate binding and metal interaction on the same print molecule if this is e.g. a glycoproten with surface-bound histidines.

As print molecule (imprinting molecule) for prearrangement of the ligands, the invention preferably uses biological macromolecules, e.g. enzymes, antibodies, glycoproteins or other proteins, nucleic acids, polysaccharides. The molecular imprinting is preferably carried out in aqueous media which are the normal surroundings of these molecules. It has also become apparent that larger or smaller amounts of organic solvents which are miscible with water, such as DMF (dimethylformaide), DMSO (dimethylsulforide), formamide (M. St{dot over (a)}hl, M. O. M{dot over (a)}nsson, K. Mosbach, Biotechn. Lett., 12 (1990) 161; N. Chang, S. J. Hen, A. M. Klibanov, BBRC, 176 (1991) 1462), may be added. In some cases, also pure DMSO can be used, in which protein and a monomer mixture (the ligands) are dissolved. A polymerised product is obtained, having a sufficient amount of correctly positioned, binding groups to provide a certain selectivity.

Matrix materials which are useful according to the invention must contain surface-bound reactive groups which can react with and covalently bind prearranged ligands. The matrices may be solid or in the form of gels and comprise particles, chips, electrodes, gel etc. Suitable matrix materials are silica (particles, chips etc.), glass (particles, electrodes etc.), biological polymers (agarose, dextran, gelatin etc.) and synthetic polymers (polyvinyl alcohol, TRIM (P. Reinholdsson, T. Hargitai, B. Törnell, R. Isaksson, Angew. Macromol. Chem., 1991, in press) etc.) When the matrix consists of a particulate solid phase, the surface is to be found both on the outside of the particles and on the surface of the pores thereof. In most cases, the latter surface is many times larger than the former.

Reactive groups on the matrix material can be acrylate, methacrylate. vinyl, hydroxyl or silanol.

If the matrix material contains no suitable reactive groups, it may be derivatised in advance with suitable groups, such as methacryl groups, before immobilising the ligands on the matrix.

The invention will now be described in more detail by means of the following, non-restrictive Example.

EXAMPLE

Methcrylate Silica

3-methacryloyloxypropyltrimethoxysilane (2.0 g, 8.1 mmol, Fluka) was mixed with 100 ml of water and dissolved during powerful stirring by means of a magnetic stirrer at 22° C. for 4 h. Porous silica (5.0 g, “Lichrospher Si 300”, Merck) was suspended in 20 ml of water and treated with vacuum and ultrasonics, thereby producing pores free from air. Subsequently, the silane solution was added, and the silanisation was allowed to proceed for 4 h at 60° C. in a round-bottomed flask placed In a water bath and fitted with a TEFLON, tetrafluoroethylene fluorocarbon polymer, which is a trademark of Dupont Chemical Company—coated blade mixer. The derivatised silica was washed on a glass filter with water and methanol and then air-dried on the filter.

Titration with bromine water (according to Glad et al, J. Chromatogr., 347 (1985) 11) yielded 335 μmol of methacrylate groups per g of silica product. A carbon analysis yielded 620 μmol of silane per g of silica product, which indicates that more than half of the groups are still reactive to subsequent immobilisation.

Preparation

Mixtures according to the Table below with RNase B and STI (Soybean trypsine inhibitor), respectively, as print molecule.

mg μmol Methacrylate-silica 800 268 Vinyl imidazole¹⁾ 0.39 4.14 Acrylphenyl boric acid 1.59 8.32 Acrylamide 100 1410 PDA (piperazine diacrylamide) 50 257 TEMED (N,N,N′,N′- 5 tetramethylenediamine) ZnCl₂ 0.64 4.70 Water/DMF (7/3, w/w) 2.5 ml Ammonium persulphate alt. A) RNase B (molecular 10 0.73 weight 14700) alt. B) STI (molecular 10 0.53 weight 20100) ¹⁾ref. C. G. Overberger, N. Vorchheimer, JACS, 85 (1963) 951

After mixing the respective print molecule with all the other ingredients in a total of 2.5 ml of water/DMF, the samples were cooled, and then N₂ gas was conducted through the mixture. After about 30 s, the mixture began to solidify. The preparation was allowed to stand for 1 h, and subsequently the substituted silica particles were washed on a glass filter with water/DMF. Small polymer particles were removed by sedimentation, and the remaining particles were packed in steel columns (5×0.5 cm). When injecting RNase B on preparation A, the elution was delayed as compared with preparation B.

As an alternative to vinyl imidazole, vinyl benzyl iminodiacetic acid can be used (L. R. Morris, R. A. Mock, C. A. Marshall, J. H. Howe, JACS, 81 (1959) 377). These bind metal ions, e g. Zn²⁺, and Cu²⁺, which have been used for a long time in so-called immobilised metal affinity chromatography (J. Porath, J. Carlsson, I. Olsson, G. Belfrage, Nature. 258 (1975) 598). 

1. A process for producing a molecularly imprinted adsorption material, comprising the steps of: forming non-covalent or reversible-covalent bonds between at least two ligands and a protein print molecule, said at least two ligands becoming at least two bound ligands, each one of said at least two ligands comprising at least two different functional groups, having at least one of said at least two different functional groups being an imidazole-metal, an iminodiacetic acid-metal, a carboxyl, an amine, a thiol, or an aldehyde and which is reversibly bound to said print molecule; immobilizing said at least two bound ligands to a matrix by covalently binding at least one of said at least two different functional groups to said matrix; extracting said protein print molecule from said immobilized at least two bound ligands, said extracting of said protein print molecule forming a stereo-tailored zone; producing a molecularly imprinted adsorption material.
 2. The molecularly imprinted adsorption material produced by the process of claim 1, having said functional group comprising an imidazole-metal or an iminodiacetic acid-metal and said functional group being reversibly bound to a protein print molecule.
 3. The molecularly imprinted adsorption material produced by the process of claim 1, in which said ligands are monomers and in which said immobilizing comprises a further step of polymerizing said monomers.
 4. The molecularly imprinted adsorption material produced by the process of claim 1, having said stereo-tailored zone configured to an enzyme or glycoprotein.
 5. The molecularly imprinted adsorption material produced by the process of claim 1, having said matrix formed through the polymerization of said different functional groups into a cross-linked polymer.
 6. The process according to claim 1, further comprising the step of: forming said matrix through the polymerization of said different functional groups into a cross-linked polymer.
 7. The process according to claim 1, further comprising the step of: binding at least one of said at least two different functional groups to an already existing matrix.
 8. A molecularly imprinted adsorption material for adsorbing protein molecules comprising: a matrix, at least two ligands covalently bound to the surface of said matrix by directed immobilization forming at least two immobilized ligands, in which each of said at least two ligands include at least two different functional groups, in which at least one of said at least two different functional groups is an imidazole-metal or an iminodiacetic acid-metal, a molecularly imprinted stereo-tailored zone.
 9. The molecularly imprinted adsorption material of claim 8, having said matrix comprising a silica, a glass, or mixtures thereof.
 10. The molecularly imprinted adsorption material of claim 8, having said matrix comprising a methacrylate-silica material.
 11. The molecularly imprinted adsorption material of claim 8, having said matrix comprising an acrylate or a methacrylate surface bound reactive group.
 12. The molecularly imprinted adsorption material of claim 8, having the adsorption material stereo-tailored to selectively adsorb a protein.
 13. The molecularly imprinted adsorption material of claim 8, having the adsorption material stereo-tailored to selectively adsorb an enzyme.
 14. The molecularly imprinted adsorption material as claimed in claim 8, having said matrix comprising a silica, a silane and a derivatized vinyl monomer.
 15. The molecularly imprinted adsorption material of claim 8, having said matrix comprising a biological polymer, a synthetic polymer, or mixtures thereof.
 16. The molecularly imprinted adsorption material of claim 8, having said matrix comprising a monomer.
 17. The molecularly imprinted adsorption material of claim 8, having said matrix comprising a vinyl surface bound reactive group.
 18. The molecularly imprinted adsorption material of claim 8, having said matrix comprising a hydroxyl surface bound reactive group.
 19. The molecularly imprinted adsorption material of claim 8, having said matrix comprising a silanol surface-bound reactive group.
 20. The molecularly imprinted adsorption material of claim 8, having the adsorption material stereo-tailored to selectively adsorb a nucleic acid.
 21. The molecularly imprinted adsorption material of claim 8, having the adsorption material stereo-tailored to selectively adsorb a polysaccharide.
 22. The molecularly imprinted adsorption material of claim 8, having the adsorption material stereo-tailored to selectively adsorb a glycoprotein. 